This invention pertains generally to devices and methods for the liquid separation of food pieces based upon differences in density. In particular, the present invention relates to an apparatus and method for the liquid separation of young peas from mature peas based upon their starch content.
A primary attribute of peas that is of concern to consumers is their sweetness. Pea sweetness depends upon the sugar content within the peas which is itself a function of pea maturity. Pea maturity is a measure of the starch content within the peas. As the peas mature, sugars initially present within the peas are converted to starch. This conversion occurs because starch is a better long term energy storage compound than is sugar. The amount of starch within the peas also affects the texture or mouth feel of the peas. Consumers prefer a tender mouth feel which translates into smooth, firm texture. As starch concentration increases within the peas, the peas tend to take on a tough texture.
Traditionally pea maturity (i.e., starch concentration) has been objectively calculated by a wet chemistry test that determines the percentage of Alcohol Insoluble Solids (AIS) within the pea. As a pea matures the amount of the alcohol insoluble solids within the pea increases while the amount of alcohol soluble solids decreases. AIS units represent the percentage of starch within the peas. For example, early peas which are usually high in sugar content have low starch concentrations and therefore a low AIS percentage, whereas mature peas picked later in the season have high starch concentrations and therefore a high AIS percentage. The accepted procedure for the calculation of AIS is designated as "Solids (Alcohol-Insoluble) in Frozen Peas, Gravimetric Method", 32.065 of the Association of Official Chemists. In addition to the AIS test, an instrument known as a Tenderometer (available from the FMC Corporation) is used to provide an initial rough estimation of the quality of a batch of peas based upon their relative tenderness.
As sugar is converted by the peas into starch, the density of the pea increases since starch in vivo is a more dense compound than sugar. Because of this difference in density, mature peas have been separated from young (high sugar) peas by formulating a brine solution of intermediate density calculated from data obtained by the AIS test and the use of the Tenderometer. The peas are dispensed into the static brine solution and the more mature peas with a high starch concentrations and thereby density in a high range tend to sink to the bottom of the brine solution. Younger, higher sugar peas with low starch concentrations and thereby density in a low range tend to float.
The use of a brine solution poses problems. One of these problems is the corrosion of equipment. The high salt concentration can cause metals within the pea separator to rust which may effect the taste of the peas. In addition, there is the greater problem of disposing of the brine solution after it has been used. Brine discharge could cause environmental problems by killing fish and seeping into ground water supplies. In addition, the density of the brine solution is determined for a single batch of peas. Therefore, the density of that brine solution can not be easily changed during the processing of the batch of peas to accommodate fluctuations in starch concentrations of the batch of peas during the separating process. Moreover, brine solutions of differing densities are required to separate batches of peas having different starch concentrations.
There is a continuing need for improved separation of mature peas from younger peas. In particular, there is a need for a pea separating apparatus and method that does not use a brine solution to carry out the density separation process. The pea separating apparatus should use a fluid medium that lessens the corrosion of the equipment and eliminates the disposal problem associated with brine solutions. The pea separating apparatus should readily permit adjustments to be made to the separating process to accommodate batches of peas having differing starch concentrations. Moreover, the pea separating apparatus should allow the separating process to be adjusted during the processing of a single batch of peas to accommodate starch concentration fluctuations within that batch.